In previously filed patent applications U.S. Ser. Nos. 10/986,129 and 10/683,522 and 10/665,664, polyester particles are crystallized in a liquid at a temperature above the Tg of the liquid. In many instances, the liquid vapor pressure exceeds atmospheric at such temperature, thereby requiring the application of pressure to retain the fluid in a liquid state. Upon reaching a desired degree of crystallization, the partially crystallized particles are separated from the liquid in a separation device comprising a cylindrical wire mesh into which the particles accumulated into a particle bed, with the liquid flowing into the outer annulus and discharged through a liquid outlet. The liquid outlet discharges the liquid and fines, which is then recycled back directly or indirectly to the polyester polymer underfluid cutter. Without providing a further separation technique for removing fines, the fines would eventually build up in the closed loop process and foul equipment.
The particles are discharged through a gate means which maintains the pressure within the separation device above the vapor pressure of the liquid at the liquid temperature. Illustrated as a gate means is a rotary air lock valve.
In the configuration described in one or more of the above US Patent Applications, the particle bed approaching the rotary air lock valve is submerged in water, and in one embodiment, a jet of cool water is injected into the particle bed near the rotary air lock. As a result, the particles discharged from the separation device have a water content proportional to the amount of water entrained in the gate means. The discharged particles could be sent to dryers.
It would be desirable to provide a low cost separation device which provides a solids discharge stream with lower water content. Alternatively, it would be desirable to reduce the fines content in the liquid discharge outlet.